Package-on-Package Structure with Through Molding Via

ABSTRACT

Disclosed herein is a device comprising a first package having a first side with a plurality of connectors disposed thereon and a second package mounted on the first package by the connectors. A molding compound is disposed on the first side of the first package and between the first package and the second package. A plurality of stress relief structures (SRSs) are disposed in the molding compound, the plurality of SRSs each comprising a cavity free of metal in the molding compound and spaced apart from each of the plurality of connectors.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductor layers of material over a semiconductorsubstrate, and patterning the various material layers using lithographyto form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. These smallerelectronic components also, in some instances, require smaller packagesthat utilize less area than packages of the past.

Package on package (PoP) technology is becoming increasingly popular forits ability to allow denser integration of integrated circuits into asmall overall package. PoP technology is employed in many advancedhandheld devices, such as smart phones. While PoP technology has allowedfor a lower package profile, the total thickness reduction is currentlylimited by the joint height and the distance between adjacent joints,referred to as the pitch. The PoP device is formed by stacking a packageor substrate with one or more dies on a second package, and connectingthe packages with conductive interconnects.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1A and 1B are diagrams illustrating packages with molded stressrelief structures according to an embodiment;

FIGS. 2 through 9 illustrate cross-sectional views of intermediate stepsin forming a package-on-package structure with molded stress reliefstructures according to an embodiment;

FIG. 10 is a cross-sectional diagram illustrating the structure of amolded stress relief structure according to an embodiment;

FIGS. 11A-11F illustrate layouts of molded stress relief structuresaccording to various embodiment; and

FIG. 12 is a flow diagram illustrating a method of forming apackage-on-package structure with molded stress relief structuresaccording to an embodiment.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to illustrate the relevant aspects of the embodiments and are notnecessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the present disclosure arediscussed in detail below. It should be appreciated, however, that thepresent disclosure provides many applicable concepts that can beembodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the disclosure, and do not limit the scope of the disclosure.Note that, for simplification, not all element numbers are included ineach subsequent drawing. Rather, the element numbers most pertinent tothe description of each drawing are included in each of the drawings.

FIGS. 1A and 1B are a perspective view and a top view, respectively, ofa package 100 having a molding compound 106 with stress reliefstructures (SRSs) 110 formed therein according to an embodiment of thedisclosure. A package 100 has a substrate 112 with a molding compound106 on one side. The molding compound 106 has connector openings 104with a connector 102 disposed in each connector opening 104. A die 108is mounted in the substrate 112 and embedded or otherwise disposed inthe molding compound 106. In an embodiment, the die 108 is in the centerregion of the molding compound 106. The molding compound 106 also hasone or more SRSs 110 near the interior corners of the array ofconnectors 102. The SRSs 110 are cavities within the molding compound106.

The molding compound 106, substrate 112 and die 108 may each have adifferent coefficient of thermal expansion (CTE). Thermal processing ofthe package 100 after application of the molding compound 106 may causethe different elements to expand at different rates under the heating ofthe thermal processing, possibly causing the molding compound 106 toform cracks. The stresses causing cracking has been observed to begreatest at the interior corner region of the array of the connectors102 identified as the stress region 114 in FIG. 1B. The thermal stresstends to cause cracking in the stress region 114, particularly betweenadjacent connector openings 104. Cracks in the molding compound 106 mayextend from the top surface of the molding compound 106 to the substrate112, exposing and possibly cracking traces on the surface of thesubstrate 112. Creating SRSs 110 near the stress region 114 relieves thestresses in the molding compound 106, reducing cracking of the moldingcompound 106.

FIG. 2 is a cross-sectional view illustrating a substrate 112 for apackage 100 according to an embodiment. The substrate 112 may compriseone or more substrate layers 202 having one or more conductive elements206 and one or more lands 204. While a single substrate 112 is shown inthe drawings, several substrates 112 may optionally be processed on aworkpiece (not shown) comprising a plurality of substrates 112 and theworkpiece may be singulated during a subsequent process step.

The conductive elements 206 are metal vias, traces or other conductivefeatures connecting the lands 204. In an embodiment, the substrate 112includes one or more redistribution layers (RDLs) such as dielectriclayers with one or more lands 204 which may be electrically connected bythe conductive elements 206. In other embodiments, the substrate 112 isa PCB, carrier or other structure.

FIG. 3 is a cross sectional view illustrating mounting a die 108 on thesubstrate 112 according to an embodiment. One or more dies 108 may bemounted on the lands 204. While the mounting of a single die 108 isillustrated for clarity, any number of dies 108 may be mounted to thelands 204. The die 108, in some embodiments, is mounted to the lands 204via solder balls 302 in a ball grid array, via surface mount technology,pin grid arrays, wire interconnects, conductive adhesive, a socket, oranother suitable technique.

FIG. 4 is a cross-sectional view illustrating formation of connectors102 on the top of the substrate 112 according to an embodiment. In suchan embodiment, the connectors 102 are solder balls formed on the lands204. In another embodiment, the connectors 102 are studs, pillars, bumpsor other conductive features.

FIG. 5 is a cross sectional view of a molding compound 106 formed overthe connectors 102. In an embodiment, the molding compound 106 is anonconductive material such as an epoxy, a resin, a moldable polymer, orthe like. In such an embodiment, the molding compound 106 is appliedwhile substantially liquid, and then is cured through a chemicalreaction, such as in an epoxy or resin. In other embodiments, themolding compound 106 is an ultraviolet (UV) or thermally cured polymerapplied as a liquid, gel or malleable solid. In another embodiment, themolding compound 106 is a non-adhesive dry film layer.

In one embodiment, a mold is provided and the mold retains and shapesthe molding compound 106 during application and curing. For example, amold may have a border or other feature for retaining the moldingcompound 106 material when applied. The mold may comprise a release filmto assist in parting the mold from the molding compound 106. Forexample, the release film is used in embodiments where the moldingcompound 106 is an epoxy or resin to prevent the molding compound 106material from adhering to the mold surface.

In an embodiment, the molding compound 106 is formed covering theconnectors 102 and the die 108 has a top surface exposed. In anotherembodiment, the die 108 is covered by the molding compound 106, and inanother embodiment, the connectors 102 are exposed through the surfaceof the molding compound 106 after forming the molding compound.

FIG. 6 is a cross-sectional view illustrating patterning of the moldingcompound 106 according to an embodiment. The molding compound 106 mayhave portions removed to form SRS 110 openings that, in an embodiment,are empty or free of metal features or connectors 102. Additionally, themolding compound 106 is removed over and around the connectors 102 toform the connector openings 104. In an embodiment, the SRSs 110 extendfrom the top surface of the molding compound 106 through the moldingcompound 106. In such an embodiment, the SRSs 110 each extend to thesubstrate 112. In another embodiment, the SRSs 110 extend partiallythrough the molding compound 106, with a portion of the molding compound106 forming the lowest or bottom surface of the SRS 110 so that part ofthe molding compound 106 is disposed between the SRS and the substrate112.

In an embodiment, the molding compound 106 is removed by laser ablationto form the connector openings 104 and SRSs 110. In such an embodiment,a laser is used to form the connector openings 104 and the SRSs 110 byburning off or ablating the molding compound 106. The depth of theopenings is controlled by the power of the laser, the speed at which thelaser is moved or other processing factors. For example, a laser mayhave a cutting beam with a width smaller than the desired connectoropening size, and may forming an opening by cutting a path in themolding compound. The laser is moved over the center portion of aconnector 102 at a first, fast speed since the molding compound isthinner than other portions of the intended connector opening 104. Thelaser may be moved at a second, slower speed at the edges of theconnectors 102, where the amount of molding compound removed is greaterand where deeper cutting by the laser is required to achieve the desireddepth.

In other embodiments, the molding compound 106 is patterned, forexample, by etching the molding compound, by molding the moldingcompound 106 to shape while the molding compound 106 is in a liquidform, through milling or drilling or by another suitable process.

In an embodiment, the SRSs may be formed using the same process as theconnector openings 104. Thus, the SRSs 110 may be formed using laserablation. In another embodiment, the SRSs 110 are formed separately,either before or after the connector openings 104 are formed. In such anembodiment, the SRSs 110 may be formed using a different technique thanthe connector openings 104. For example, the connector openings 104 areformed during molding of the molding compound 106, and the SRSs 110 aresubsequently formed with laser ablation.

In an embodiment, the connector openings 104 and SRSs 110 are round andformed with sloping sides, resulting in a conical shape. However, theconnector openings 104 and SRSs 110 may each have a non-conical shape.For example, the connector openings 104 may be formed to conform to theshape of the connector 102. In such an example, square connectors may bedisposed in a square or substantially square connector opening. Inexample, the SRSs 110 may be oblong, rectangular irregular or any othershape. Additionally, while a single SRS 110 is illustrated as beingdisposed near a group of connectors 102, in an embodiment, multiple SRSs110 are used to effectively reduce strain in the molding compound 106.

FIG. 7 is a cross-sectional view illustrating application of packageconnectors 702 to the substrate 112. One or more package connectors 702are formed on the bottom side of the substrate 112 on the lands 204,resulting in a device configured to be mounted to another board,package, carrier, PCB or the like. In an embodiment, the packageconnectors 702 are solder balls. In other embodiments, the packageconnectors 702 are bumps, studs, pillars, land grid array (LGA)elements, pins or another conductive feature.

FIGS. 8 and 9 are cross sectional views illustrating application of asecond package 802 to the package 100 according to an embodiment. Thesecond package 802 has, for example, a substrate 808, such as aninterposer, package substrate, another die, carrier or the like, withone or more dies 804 mounted thereon by way of a mount 806 such as anadhesive, underfill, solder ball grid or the like. One or more packagemounts 812 are disposed along a bottom surface of the second package802. In an embodiment, the substrate 802 has one or more conductiveelements 810 disposed in an insulating layer 808 such as a dielectric,oxide, resin, PCB or other electrically insulating material. Conductiveelements 810 are disposed in the insulating layer 808 and electricallyconnect the package mounts 812 to the dies 804.

The second package 802 is mounted on the package 100; with theconnectors 102 contacting the package mounts 812. In an embodiment, theconnectors 102 and package mounts 812 are solder balls, and the secondpackage 802 is mounted to the package 100 by reflowing the solder ballsto form a joint 902. In another embodiment, the package mounts 802 arestuds, bumps, pillars or the like, and the second package 802 is joinedto the package 100 by soldering the package connectors 812 to thepackage 100. In yet another embodiment the second package 802 is joinedto the package 100 by a land grid array and lands, by pins and a socket,or by another conductive structure.

FIG. 10 is a cross-sectional diagram illustrating the structure of a SRS110 according to an embodiment. In an embodiment, the molding compound106 is on a finishing layer 1004 such as a polymer, oxide, nitride, orthe like and has a thickness between about 120 μm and about 140 μm. Thefinishing layer 1004 is on a protection layer 1002 such as a passivationlayer or the like.

The connector opening 104 has a bottom width 1008 that is about the sameor greater than the width 1006 of the connector 102. In someembodiments, the SRS 110 is about the same size or same shape as theconnector opening 104. In an embodiment, the connector width 1006 isabout and about 170 μm and about 230 μm, the connector opening bottomwidth 1008 and SRS bottom width are between about 190 μm and about 250μm, and the connector opening top width 1010 and SRS top width 1016 arebetween about 370 μm and about 430 μm.

The SRS 110 is spaced apart from the connector opening 104 so that anymisalignment or error in the placement of the laser during moldingcompound 106 surface formation is accounted for. Additionally, spacingthe SRS 110 apart from the connector opening 104 provides greaterstrength to the molding compound 106 around the connector opening 104.The size and spacing of the SRSs 110 is determined by the thickness ofthe molding compound 106, the pitch of the connector openings 104, theCTEs of the structures forming the package 100. In particular, the SRS110 is spaced apart from the connector opening 104 by separationdistance of at least 30 μm.

The molding compound 106 is provided on the substrate 112 in part toprevent warpage of the substrate 112. The total surface area of the SRSs110 is between about 0.01% and about 15% of the surface area of themolding compound 106. In such an embodiment, the surface area of theSRSs 110 is determined by the area of the molding compound 106 omittedto form the SRSs 110. Additionally, the volume of each SRS 110 isbetween about 8×10⁻⁶ mm³ and about 5 mm³. Limiting the volume and tototal surface area of the SRSs 110 prevents weakening of the moldingcompound 106 and maintains the molding compound 106 support of thesubstrate.

FIGS. 11A, 11B and 11C illustrate top views of embodiments of SRS 110arrangements in relation to the array of connectors 102. As shown inFIG. 11A, in an embodiment, a single SRS 110 is disposed in theconnector 102 array interior corner region between the die 108 (See,e.g., FIGS. 1A-1B, 3-9) and the connectors 102, with the SRS 110 havinga size or width smaller than the connector opening 104. In such anembodiment, the SRS 110 may have the same shape as the connector opening104.

FIG. 11B shows an embodiment with multiple SRSs 110 disposed in theconnector 102 array interior corner region between the die 108 (See,e.g., FIGS. 1A-1B, 3-9) and the connectors 102. The SRSs 110 are shownhaving a size or width smaller than the connector opening 104, thoughother sizes and shapes may be used. FIG. 11C shows an embodiment withone or more SRSs 110 disposed in the interior corner region of the arrayof connectors 102 and between the connectors 102.

FIGS. 11D, 11E and 11F illustrate top views various shaped of SRSs 110according to embodiments. As shown in FIG. 11D, in an embodiment, an SRS110 may have two or more connectors 102 disposed therein, with the wallsof the SRS 110 separate from the connectors 102 and a gap or space inthe molding compound 106 between two of the connectors 102. FIG. 11Eshows an embodiment in which the SRS 110 is a partial ring disposed inthe interior corner region of the array of connectors 102 between thedie 108 (See, e.g., FIGS. 1A-1B, 3-9) and the connectors 102. FIG. 11Fshows an embodiment of an SRS 110 with an angled shape disposed in theinterior corner region of the array of connectors 102 between the die108 (See, e.g., FIGS. 1A-1B, 3-9) and the connectors 102. It should benoted while embodiments of the SRSs 110 are shown here with a partialring or an angled shape; the SRSs 110 can be shaped in to circle, oval,rectangle, ring, triangle, diamond, or other regular or irregular shape.

FIG. 12 is a flow diagram illustrating a method 1200 of forming apackage-on-package structure with SRSs according to an embodiment. Asubstrate is provided in block 1202 and one or more dies attached to thesubstrate in block 1204. Connectors are formed on the substrate in block1206 and molding compound is applied in block 1208. The surface of themolding compound is formed in block 1210, exposing the connectors andforming one or more SRSs. One or more mounts are formed in block 1212 onthe substrate opposite the die. A second package is applied in block1214 to the package and over the molding compound.

Thus, a device according to an embodiment comprises a substrate having afirst side with a plurality of connectors and a die disposed thereon andmolding compound disposed on the first side and surrounding each of theplurality of connectors. A stress relief structure (SRS) is disposed inthe molding compound, the SRS comprising a cavity in the moldingcompound separate from each of the plurality of connectors.

A device according to another embodiment comprises a first packagehaving a first side with a plurality of connectors disposed thereon anda second package mounted on the first package by the connectors. Amolding compound is disposed on the first side of the first package andbetween the first package and the second package. A plurality of stressrelief structures (SRSs) are disposed in the molding compound, theplurality of SRSs each comprising a cavity free of metal in the moldingcompound and spaced apart from each of the plurality of connectors.

A method according to an embodiment comprises forming a molding compoundon a first side of a first package and around each of a plurality ofconnectors on the first side of the first package, and forming aplurality of stress relief structures (SRSs) in the molding compound,the plurality of SRSs each comprising a cavity in the molding compoundfree of metal and spaced apart from each of the plurality of connectors.

Although embodiments of the present disclosure and their advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims. For example, it will be readily understood by those skilled inthe art that many of the features, functions, processes, and materialsdescribed herein may be varied while remaining within the scope of thepresent disclosure. Moreover, the scope of the present application isnot intended to be limited to the particular embodiments of the process,machine, manufacture, composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosure of the present disclosure,processes, machines, manufacture, compositions of matter, means,methods, or steps, presently existing or later to be developed, thatperform substantially the same function or achieve substantially thesame result as the corresponding embodiments described herein may beutilized according to the present disclosure. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

What is claimed is:
 1. A device comprising: a substrate having a firstside with a plurality of connectors and a die disposed thereon; moldingcompound disposed on the first side and surrounding each of theplurality of connectors; and a stress relief structure (SRS) disposed inthe molding compound, the SRS comprising a cavity in the moldingcompound separate from each of the plurality of connectors.
 2. Thedevice of claim 1, further comprising a plurality of connector openingsin the molding compound, each of the plurality of connectors disposed ina respective one of the plurality of connector openings, wherein the SRSis separated from the plurality of connector openings.
 3. The device ofclaim 1, wherein the SRS is disposed between the plurality of connectorsand the die.
 4. The device of claim 1, wherein the SRS has a conicalshape.
 5. The device of claim 1, wherein the die is disposed in a centerregion of the plurality of connectors, and wherein the SRS is disposedadjacent to an interior corner region of the plurality of connectors. 6.The device of claim 1, further comprising a package mounted over thesubstrate, the molding compound disposed between the substrate and thepackage, wherein each of the plurality of connectors extend between thesubstrate and the package.
 7. A device comprising: a first packagehaving a first side with a plurality of connectors disposed thereon; asecond package mounted on the first package by the connectors; a moldingcompound disposed on the first side of the first package between thefirst package and the second package; and a plurality of stress reliefstructures (SRSs) disposed in the molding compound, the plurality ofSRSs each comprising a cavity free of metal in the molding compound andspaced apart from each of the plurality of connectors.
 8. The device ofclaim 7, further comprising a die mounted to the first side of the firstpackage, the plurality of connectors disposed around the die, each ofthe plurality of SRSs between one or more of the plurality of connectersand the die.
 9. The device of claim 7, further comprising a plurality ofconnector openings in the molding compound, each of the plurality ofconnectors disposed in a respective one of the plurality of connectoropenings, wherein each of the plurality of SRSs are separated from theplurality of connector openings.
 10. The device of claim 9, wherein eachof the plurality of SRSs has a same shape as one of the plurality ofconnector openings.
 11. The device of claim 7, wherein at least one ofthe plurality of SRSs has a conical shape.
 12. The device of claim 9,wherein each of the plurality of SRSs is spaced at least 30 μm away fromeach of the plurality of connector openings.
 13. The device of claim 12,wherein a total surface area of the plurality of SRSs is between about0.01% and about 15% of the surface area of the molding compound.
 14. Amethod of forming a device, comprising: forming a molding compound on afirst side of a first package and around each of a plurality ofconnectors on the first side of the first package; and forming aplurality of stress relief structures (SRSs) in the molding compound,the plurality of SRSs each comprising a cavity in the molding compoundfree of metal and spaced apart from each of the plurality of connectors.15. The method of claim 14, further comprising mounting a die to thefirst side of the first package, and wherein the forming the moldingcompound comprises forming molding compound around the die.
 16. Themethod of claim 15, wherein the plurality of connectors are disposedaround the die, and wherein each of the plurality of SRSs are formedadjacent to an interior corner region of the plurality of connectors andbetween the interior corner region of the plurality of connectors andthe die.
 17. The method of claim 14, further comprising forming aplurality of connector openings in the molding compound, each of theplurality of connectors disposed in a respective one of the plurality ofconnector openings, wherein each of the plurality of SRSs are separatedfrom the plurality of connector openings.
 18. The method of claim 17,wherein the forming the plurality of SRSs and the forming the pluralityof connectors openings comprise removing a portion of the moldingcompound.
 19. The method of claim 18, wherein the removing a portion ofthe molding compound comprises removing the portion of the moldingcompound by laser ablation.
 20. The method of claim 14, wherein each ofthe plurality of SRSs is formed to have a shape comprising a square,circle, oval, rectangle, ring, triangle, diamond, or an irregularpolygon.